So, with very little knowledge or experience on the subject, I wanted to look into the process of making normal/parallax/specular maps for existing textures. Given that I lack any artistic ability I eventually wanted to see if the process is automatable. I used gimp's normalmap plugin but noticed that the results came out wrong. Half the plane was fully lit and the other half not at all. After an embarrassing amount of experimentation I came to the conclusion that the normals were being interpreted at a slight angle which I could correct by adding 55 points to the green and red channel. I checked work by other texturers and by sampling their pixels I thought that their vectors look orthogonal. The question is what issue am I stumbling on that makes angling the vectors necessary? As a side note why are terrain textures displayed inverted?

I'm attaching a couple of textures I made, based on Tyddyy's excellent terrain textures, if somebody has an idea of what I'm doing wrong, possibly as advice to anyone else who might stumble on this. Also assuming they display correctly to other people as well, I think they came out ok looking.

Ooops, I'm so sorry. I'm moving this saturday, so my head is full of everything I need to get done.

Anyway, these normal map texture files look way too bright to me. Have a look at this normal map from my Hlaalu pack:

It is a lot darker and more saturated in general. Might have something to do with color profiles maybe, I had loads of problems with that when I started out. Your .dds files shouldn't have color profiles at all actually.

I believe the problem must be in the settings of the gimp-plugin or with the color profiles. I haven't used GIMP very much at all, so I can't really say how to fix either of those might-be problems I'm afraid. What OS are you on? If Windows, I'd recommend you to download the trial version of CrazyBump. It is a great tool, but quite expensive. When my trial version ran out, I bought a program called MindTex2 from steam, which is a lot cheaper, and almost as good. Still only Windows though as far as I know.

If you're on Linux, there's a program called AwesomeBump, which is open source, but I never really got a grip on how to use it. It's not very user friendly compared to the previous two.

Another tip while I'm at it: Your normal maps are very tiny compared to the diffuse maps. I'd recommend you to go for at least 512x512, or preferably the same size as your diffuse. A low res normal map will result in visible pixels when light shines on the object. Also, you get more sweet details to push out with higher res. A non-pro opinion from me. If a professional graphic artist reads this and think I put too much detail into the normal maps, then I'm wrong and you should listen to that person instead!

Thanks for looking into it lysol, you prompted me by stroke of luck to figure out what's wrong. I tried to reproduce the issue with a new texture and couldn't and I found out why. Mipmaps, apparently. I don't know if we are using mipmaps in any way, but generating mipmaps for a normal map seems to cause the texture to be rendered at an angle. Without that the plane is lit properly. Maybe someone that understands better the inner workings of our graphics engine can weigh in on that.

Anyway, these normal map texture files look way too bright to me

That was my color correction to make them look right, adding to the green and red channels to correct the angled vectors.

Another tip while I'm at it: Your normal maps are very tiny compared to the diffuse maps.

Since I used a lot of gaussian blur to remove bumps I didn't like, I assumed downscaling a blurry image to save space would have no effect detail, and I didn't notice any, although that doesn't say much. The textures don't use any compression though since I didn't know which one to choose.

Regarding the recommendations for tools, thanks for the suggestions. I've also heard of Insane Bump for gimp which seems to be pretty cool. I will have to look into them in a few months when I'm finished with some obligatory obligations.